Radiation detector

ABSTRACT

Regarding to the radiation detector  10 , which has the scintillator  16  placed on the light incidence plane plate member of the photomultiplier tube by use of the optical binder  14  interposed therebetween, and which includes a coated film FLM formed so as to cover the scintillator and at least part of the side tube portion  12   b  of the photomultiplier tube, since the scintillator and the photomultiplier tube are strongly fixed to each other by use of the coating film FLM, so that the size increase of the radiation detector can be suppressed.

TECHNICAL FIELD

[0001] The present invention relates to a radiation detector.

BACKGROUND ART

[0002] As a radiation detector of a combination of a photomultipliertube and a scintillator, for example, a radiation detector as disclosedin Japanese Patent Laid-Open No. Shou62(1987)-59884 gazette has beenknown.

[0003]FIG. 5 is a view illustrating a radiation detector 1 described inthe said gazette. The radiation detector 1 has a constitution, in whicha metallic container 3 accommodating a scintillator 2 is fixed to afaceplate, a light incidence plane plate member 5 a of a photomultipliertube 5 with an optical binder 4 interposed therebetween. The opticalbinder 4 also functions as adhesive.

[0004] On one of end of the metallic container 3, which is placed on aside of the light incidence plane plate member 5 a of thephotomultiplier tube 5, a light emission window 6 made of glass isapplied. Accordingly, when radiation is incident on the scintillator 2,light is generated. Then the light is incident on the light incidenceplane plate member 5 a via the light emission window 6 and the opticalbinder 4 into the photomultiplier tube 5, where the light is convertedinto electric signals, which are amplified by the photomultipliersection 5 c and focused on an anode 5 d.

DISCLOSURE OF THE INVENTION

[0005] However, the radiation detector according to the above describedconventional art had a problem described below. Specifically, theradiation detector according to the above described conventional arttends to be large, since the scintillator accommodated in the metalliccontainer is fixed to the photomultiplier tube. More specifically, ifthe diameter of the scintillator is to be adjusted to the diameter ofthe light incidence plane plate member of the photomultiplier tube, thediameter of the metallic container should be designed larger than thatof the scintillator. Moreover, it may be possible that the diameter ofthe metallic container is matched to the diameter of the light incidenceplane plate member of the photomultiplier tube. In this case, thediameter of the scintillator becomes smaller than that of the lightincidence plane plate member, so that radiation detection efficiencydeclines.

[0006] In the above described radiation detector, it is requested inmany cases that, after the metallic container accommodating thescintillator and the photomultiplier tube are fixed with the opticalbinder interposed therebetween, the metallic container accommodating thescintillator and the photomultiplier tube are strongly fixed by use of ametallic case or the like which covers the metallic containeraccommodating the scintillator and the photomultiplier tube. In such acase, the radiation detector further increases in size.

[0007] Therefore, an object of the present invention is to provide aradiation detector which solves the problem mentioned above, in which ascintillator and a photomultiplier tube can be strongly fixed, and whichis small in size.

[0008] In order to solve the above described problem, the radiationdetector according to the present invention, which has the scintillatorplaced on the light incidence plane plate member of the photomultipliertube with the optical binder interposed therebetween, is characterizedby including a coated film formed so as to cover the scintillator and atleast part of the side tube portion of the photomultiplier tube.

[0009] Since the coated film is formed so as to cover the scintillatorand at least part of the side tube portion of the photomultiplier tube,the scintillator and the photomultiplier tube can be strongly fixed toeach other. Various structures of the coated films are possible. Sincethe scintillator and the photomultiplier tube are strongly fixed to eachother by the coated film, the size increase of the radiation detectorcan be suppressed, and the radiation detector can be constituted insmall size.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a sectional view of a radiation detector according to afirst embodiment of the present invention.

[0011]FIG. 2 is a partial enlarged sectional view of the radiationdetector according to the first embodiment of the present invention.

[0012]FIG. 3 is a partial enlarged sectional view of a radiationdetector according to a second embodiment of the present invention.

[0013]FIGS. 4A, 4B, and 4C are views showing multi-layer structures of acoated film FLM.

[0014]FIG. 5 is a sectional view of a radiation detector according tothe conventional art.

BEST MODES OF CARRYING OUT THE INVENTION

[0015] A description about a radiation detector according to a firstembodiment of the present invention will be made with reference to thedrawings. First, a constitution of the radiation detector of theembodiment will be described.

[0016]FIG. 1 is a sectional view of the radiation detector according tothe present invention. FIG. 2 is a partial enlarged sectional view ofthe radiation detector according to the embodiment.

[0017] As illustrated in FIGS. 1 and 2, the radiation detector 10according to this embodiment includes a photomultiplier tube 12, ascintillator 16 placed on a light incidence plane plate member 12 a ofthe photomultiplier tube 12 with an optical binder 14 interposedtherebetween, a first layer film (first organic film in this example) 18formed so as to cover the scintillator 16 and at least part of a sidetube portion 12 b, a first intermediate layer film (metallic film inthis example) 20 formed on the outside of the first layer film 18, and asecond layer film (second organic film in this example) 22 formed on theoutside of the intermediate layer film 20. In FIG. 1, for the sake ofconvenience, the first layer film 18, the first intermediate layer film20, and the second layer film 22 are illustrated as a single layer filmFLM. Each component will be described in detail below.

[0018] As shown in FIG. 1, the photomultiplier tube 12 has a structure,in which a photomultiplier section 12 c is incorporated in an airtightcontainer including the light incidence plane plate member 12 a and theside tube portion 12 b. On an inner surface of the light incidence planeplate member 12 a, a bialkali photoelectric surface 12 d using alkalimetal such as Na, K, Rb, and Cs is formed. Note that the photoelectricsurface 12 d may use Sb and alkali metal or the like. A predeterminedelectric potential is given on the photoelectric surface 12 d via afocusing electrode 12 m made of Al vapor-deposited on an inner surfaceof the side tube portion 12 b. The photoelectric surface 12 d outputsphotoelectrons along with an amount of incident light on the lightincidence plane plate member 12 a. The photoelectrons outputted from thephotoelectric surface 12 d are amplified by the photomultiplier section12 c and gathered by an anode 12 e located at the end of thephotomultiplier section 12 c.

[0019] On an outer surface of the light incidence plane plate member 12a of the photomultiplier tube 12, the scintillator 16 is arranged by useof the optical binder 14 interposed therebetween.

[0020] The optical binder 14 fills a gap between the light incidenceplane plate member 12 a of the photomultiplier tube 12 and thescintillator 16, and eases change in refractive index given by the lightwhich is incident on the light incidence plane plate member 12 a of thephotomultiplier tube 12 from the scintillator 16.

[0021] The optical binder 14 also has a function of adhesion of thelight incidence plane plate member 12 a of the photomultiplier tube 12with the scintillator 16, although the function is insufficient. As theoptical binder 14, silicone oil (for example, Toray Dow Corning SH200(refractive index: 1.375-1.404), Shinetsu silicone oil KF96 (refractiveindex: 1.374-1.404)), silicone oil compound (for example, optseal(refractive index: 1.469), silicone gel (for example, Toray Dow CorningSE188), silicone rubber (for example, Toray Dow Corning JCR6122,Shinetsu Corning KE420/KE1800, GE silicone RTV656), and the like can belisted.

[0022] The scintillator 16 is composed of NaI(Tl), CsI(Na), CsI(Tl), orthe like. Particularly, the scintillator 16 is formed depending on aportion (effective light receiving surface) where the photoelectricsurface 12 d is formed.

[0023] The first layer film 18 is made of poly-para-xylylene. As shownin FIG. 2, the first layer film 18 is formed in close contact with thescintillator 16 and the side tube portion 12 b of the photomultipliertube 12 so as to cover the scintillator 16 and approximately one fifthof the upper portion of the side tube portion 12 b of thephotomultiplier tube 12 (on a side of the light incidence surface platemember 12 a).

[0024] On the outside of the first layer film 18, the first intermediatelayer film 20 is formed. The first intermediate layer film 20 is made ofaluminum and formed in close contact with the first layer film 18 so asto cover the first layer film 18. The first intermediate layer film 20also functions as a reflecting film for light generated by thescintillator 16.

[0025] On the outside of the first intermediate layer film 20, thesecond layer film 22 is formed. The second layer film 22 is made ofpoly-para-xylylene and formed in close contact with the firstintermediate layer film 20 so as to cover the first intermediate layerfilm 20. The second layer film 22 also has a function to preventpeel-off of the first intermediate film 20.

[0026] Next, a description will be made on a method of manufacturing theradiation detector according to this embodiment. In order to manufacturethe radiation detector 10 according to this embodiment, first, thesurface of the side tube portion 12 b of the photomultiplier tube 12 isroughened by sandblast. The roughening of the surface of the side tubeportion 12 b is for making the close contact easier between the firstlayer film 18 and the surface of the side tube portion 12 b of thephotomultiplier tube 12.

[0027] Subsequently, the scintillator 16 is arranged on the lightincidence plane plate member 12 a of the photomultiplier tube 12 by useof the optical binder 14 interposed therebetween. Here, if a materialhaving also an adhesive function is selected as the optical binder 14,(for example, silicone rubber), the light incidence plane plate member12 a of the photomultiplier tube 12 and the scintillator 16 are easilyfixed.

[0028] Subsequently, poly-para-xylylene layer is prepared by vapordeposition on the whole of the scintillator 16 and the side tube portion12 b of the photomultiplier tube 12 to form the first layer film 18.Then, aluminum is vapor-deposited on the first layer film 18 to form thefirst intermediate layer film 20. After the preparation of the firstintermediate layer film 20, poly-para-xylylene layer is again preparedby vapor deposition on the first intermediate layer film 20 to form thesecond layer film 22. Finally, the first layer film 18, the firstintermediate layer film 20, and the second layer film 22 formed on anunnecessary portion (for example, on a lower part of the side tubeportion 12 b of the photomultiplier tube 12) are cut off and removed,thus the radiation detector 10 is completed.

[0029] Next, a description will be made referring a function and aneffect of the radiation detector according to this embodiment. In theradiation detector 10 according to this embodiment, the scintillator 16is placed on the light incidence plane plate member 12 of thephotomultiplier tube 12 with the optical binder 14 interposedtherebetween, and the first layer film 18 is formed so as to cover thescintillator 16 and part of the side tube portion 12 b of thephotomultiplier tube 12. Accordingly, the scintillator 16 and thephotomultiplier tube 12 can be fixed by the first layer film 18.

[0030] Moreover, regarding the radiation detector 10 according to thisembodiment, the first intermediate layer film 20 is additionally formedon the outside of the above described first layer film 18, and thesecond layer film 22 is further formed on the outside of the firstintermediate layer film 20. Accordingly, the scintillator 16 and thephotomultiplier tube 12 can be strongly fixed by the first intermediatelayer film 20 and the second layer film 22.

[0031] In terms of the radiation detector 10 according to thisembodiment, the scintillator 16 and the photomultiplier tube 12 arefixed by a film such as the first layer film 18, the first intermediatelayer film 20, and the second layer film 22. Accordingly, the radiationdetector 10 can be constituted so as not to increase in external sizevery much. In other words, the radiation detector 10 can be constitutedin small size.

[0032] In terms of the radiation detector 10 according to thisembodiment, since the scintillator 16 and the photomultiplier tube 12are fixed by a film such as the first layer film 18, the firstintermediate layer film 20, and the second layer film 22, the shape ofthe scintillator 16 is designed comparatively freely, compared with theconventional radiation detector in which the metallic containeraccommodating the scintillator is fixed onto the photomultiplier tube.Moreover, the radiation detector 10 is sensitive to low energy radiationand the radiation detector 10 can be manufactured in low cost.

[0033] The radiation detector 10 according to this embodiment, since thefirst layer film 18 and the second layer film 22 are formed usingpoly-para-xylylene which is excellent in dampproof property, effectivelyprevents deliquesce of the scintillator 16.

[0034] Next, a description will be made of a radiation detectoraccording to a second embodiment of the present invention with referenceto the drawings. FIG. 3 is a partial enlarged sectional view of theradiation detector according to this embodiment. The structuraldifference between a radiation detector 30 according to this embodimentand the radiation detector 10 according to the first embodiment is thatthe radiation detector 30 according to this embodiment includes a secondintermediate layer film (transparent inorganic film) 24 formed on theoutside of the second layer film 22 and a third layer film (thirdorganic film) 26 formed on the outside of the second intermediate layerfilm 24.

[0035] The intermediate layer film 24 is made of SiO₂ and formed inclose contact with the second layer film 22 so as to cover the secondlayer film 22. The third layer film 26 is made of poly-para-xylylene andformed in close contact with the second intermediate layer film 24 so asto cover the second intermediate layer film 24. In this embodiment, thesecond intermediate layer film 24 is prepared by depositing SiO₂ on thesecond film 22 by vapor deposition. The third layer film 26 is formed byvapor deposition of poly-para-xylylene on the second intermediate layerfilm 24.

[0036] The formation of the second intermediate layer film layer 24 andthe third layer film 26 can make the scintillator 16 and thephotomultiplier 12 fix furthermore strongly to each other.

[0037] In the radiation detector 30 according to this embodiment, on thescintillator 16 and part of the tube side portion 12 b of thephotomultiplier tube 12, the first layer film 18, the first intermediatelayer film 20, the second layer film 22, the second intermediate layerfilm 24, and the third layer film 26 are formed in this order. Instead,these layer films may be formed in the order of the first layer film 18,the second intermediate layer film 24, the third layer film 26, thefirst intermediate layer film 20, and the second layer film 22.

[0038] In the radiation detectors 10 and 30 according to the aboveembodiments, a lamination made of the first layer film 18, the firstintermediate layer film 20, and the second layer film 22, and alamination made of the first layer film 18, the first intermediate layerfilm 20, the second layer film 22, the second intermediate layer film24, and the third layer film 26 are respectively formed so as to coverabout a fifth of the upper part of the side tube portion 12 b of thephotomultiplier tube 12. However, the part where the films are formed isnot limited to approximately a fifth of the upper part. These films maybe formed so as to cover about the upper half of the side tube portion12 b of the photomultiplier tube 12 or so as to cover the whole of theside tube portion 12 b of the photomultiplier tube 12.

[0039]FIG. 4A is a diagram illustrating a multi-layer structure of thecoated film FLM having a three layer structure shown in FIG. 1. From thescintillator 16 side, the first layer film 18, the first intermediatelayer film 20, and the second layer film 22 are sequentially laminated.

[0040] In the first embodiment, the first layer film 18 is an organicfilm, the first intermediate layer film 20 is a metallic film, and thesecond layer film 22 is an organic film. Preferably, the organic filmsare made of poly-para-xylylene, and the metallic film is made of Al. Themetallic film contains at least one of metal selected from a groupconsisting of Al, Ni, Cr, Ti, Cu, Au, and Ag, and has a function ofreflecting the scintillation light generated in the scintillator 16.

[0041] The first layer film 18 may compose of a transparent inorganicfilm. The first intermediate layer film 20 may compose of a metallicfilm, and the second layer film 22 may compose of an organic film. Thetransparent inorganic film is made of silicon dioxide (SiO₂), siliconnitride (SiN_(x)) or silicon oxynitride (SiON), and has an adhesivefunction. Preferably, the organic film is made of poly-para-xylylene,and the metallic film is made of Al. The metallic film contains at leastone of metal selected from a group consisting of Al, Ni, Cr, Ti, Cu, Au,and Ag, and the metallic film has a function of reflecting thescintillation light generated in the scintillator 16.

[0042]FIG. 4B illustrates a laminate structure of the coated film FLMhaving a four layer structure shown in FIG. 1. The difference from thatshown in FIG. 4A is that the coated film FLM includes an undercoat layerfilm UC between the scintillator 16 (and the side tube portion 12 b ofglass) and the first layer film 18. In terms of adhesive strength andlow reactivity, the material of the undercoat layer film UC ispreferably composed of Al, but may contain at least one of metalselected from a group consisting of Ni, Cr, Ti, and Cu. Furthermore, Auor Ag can be used for the material of the undercoat layer film UC.Specifically, within the organic film, openings tend to be madedepending on temperature. Gas containing water vapor penetrates throughthese openings into the first layer film 18 and comes finally into thescintillator 16. Therefore, when the metallic film is used as theundercoat layer film UC, and the organic film as the first layer film 18is formed thereon, the dampproof property can be improved. In the casewhere the inorganic layer film is formed on the organic layer film,tensile stress acts on the inorganic layer film depending ontemperature, and the inorganic layer film deteriorates. However, withthis structure, the deterioration can be suppressed.

[0043] As the undercoat layer film UC, the above described transparentinorganic film can be applied. This transparent inorganic film comprisesof silicon dioxide (SiO₂), silicon nitride (SiN_(x)), or siliconoxynitride (SiON), and has the adhesive function. Also in this case,since the undercoat layer film UC likewise functions to improve thedampproof property, the suppression of the deterioration of theinorganic layer film is possible when the inorganic layer film isprepared on the organic layer film.

[0044]FIG. 4C illustrates a laminate structure of the coated film FLM inFIG. 1, which has a five layer structure. The difference from that shownin FIG. 4A is that the second intermediate layer film 24 and the thirdlayer film 26 are provided on the second layer film 22.

[0045] In the second embodiment, the second intermediate layer film 24is a transparent inorganic film, and the third layer film 26 is anorganic film. The transparent inorganic film comprises silicon dioxide(SiO₂), silicon nitride (SiN_(x)), or silicon oxynitride (SiON), and theorganic film is made of poly-para-xylylene, thus provides strongadhesion.

[0046] The second intermediate layer film 24 may be a metallic film.Preferably, the metallic film is made of Al. The metallic film containsat least one of metal selected from a group consisting of Al, Ni, Cr,Ti, Cu, Au, and Ag, and the metallic film has a function of reflectingthe scintillation light generated in the scintillator 16. Also in thiscase, the above described undercoat layer film UC can be provided. Notethat the above described intermediate layer film may be composed of aplurality of layers.

[0047] As described above, the radiation detector 10 is a radiationdetector having the scintillator 16 placed on the light incidence planeplate member of the photomultiplier tube by use of the optical binder 14interposed therebetween, and the radiation detector 10 includes thecoated film FLM formed so as to cover the scintillator and at least partof the side tube portion 12 b of the photomultiplier tube. The side tubeportion 12 b continuously contacts with the periphery of the lightincidence plane plate member 12 a to constitute part of the vacuumcontainer. According to the radiation detector 10, the scintillator andthe photomultiplier tube are strongly fixed to each other by the coatedfilm FLM, so that the size increase of the radiation detector can besuppressed.

Industrial Applicability

[0048] The present invention is applicable for the radiation detector.

1--(amended)--. A radiation detector comprising: a scintillator placedon a light incidence plane plate member of a photomultiplier tube by usean optical binder interposed therebetween; and a coated film formed tocover the scintillator and at least part of a tube side portion of thephotomultiplier tube, wherein an outermost layer of said coated film isan organic film formed through vapor deposition.
 2. The radiationdetector according to claim 1, wherein said coated film includes a firstlayer film, a first intermediate layer film, and a second layer film,which are sequentially formed on a base material.
 3. The radiationdetector according to claim 2, wherein the first layer film is composedof an organic film, the first intermediate layer film is composed of ametallic film, and the second layer film is composed of an organic film.4. The radiation detector according to claim 3, wherein both of theorganic films are made of poly-para-xylylene, and the metallic filmcontains at least one of metal selected from a group consisting of Al,Ni, Cr, Ti, Cu, Au, and Ag.
 5. The radiation detector according to claim2, wherein the first layer film is composed of a transparent inorganicfilm, the first intermediate layer film is composed of a metallic film,and the second layer film is composed of an organic film.
 6. Theradiation detector according to claim 5, wherein the transparentinorganic film is made of any one of silicon dioxide, silicon nitride,and silicon oxynitride; the metallic film contains at lease one of metalselected from a group consisting of Al, Ni, Cr, Ti, Cu, Au, and Ag; andthe organic film is made of poly-para-xylylene.
 7. The radiationdetector according to any one of claims 2 and 5, wherein the coated filmincludes an undercoat layer film interposed between the base materialand the first layer film.
 8. The radiation detector according to claim7, wherein the undercoat layer film is a metallic film.
 9. The radiationdetector according to claim 8, wherein the metallic film is made of Al.10. The radiation detector according to claim 8, wherein the metallicfilm contains at least one of metal selected from a group consisting ofNi, Cr, Ti, and Cu.